I. Field of the Invention
The present invention relates to control devices for selective operation of electrically powered units with means for regulating the number of such units that can be operated at any one time to thus insure safety of operation, limitation of power drains or both. In particular, the invention is useful in control of any motor driven units, or solenoid operated units, or the like, such as for example, those in hospital beds, or in dispensing devices. The invention is useful in situations where it is desired to prevent more than a predetermined number of functions from being set in motion at any one time. It is particularly useful where hand operated controls are needed together with isolation of users from power circuits.
II. Description of the Prior Art
Moody, U.S. Pat. No. 3,422,318, discloses a motor starter control circuit for a series of motors in which a series of starting switch sets having electro mechanical interlocks are arranged such that when a starting switch is closed, it will connect current to interlocks on all of the other starters and to a timer which will prevent starting of any other motor for a sufficient period of time to protect against motor current overload. This circuit will not prevent subsequent starting of additional motors but will only delay motor starting so as to restrict the power drain. Further, the electro mechanical devices used alone render Moody undesirable for use in hand-held controls or where controls must be of a minimum size.
Hendrikson et al, U.S. Pat. No. 3,691,431, discloses a vending machine control arrangement which includes selection switch means and relay means which apply current to vending drives, and wherein upon actuation of one set of switch means and relay, supply to other switches and relays is cut off. This system is also not one intended for use contemplated by the instant invention and is complex in nature and employs electro-mechanical elements. Nor does it meet the size limtiations imposed upon use in such as hospital beds.
Ritzow, U.S. Pat. No. 3,671,816, shows a solid state motor control circuit wherein electrical interlocks employing diodes will divert current from other switching circuits when one switch circuit is put into operation. The circuit employs time delaying means which is designed primarily to protect against simultaneously energizing relays. The system does not contemplate continuously preventing the operation of a second relay circuit while one is in operation.
Catterall, U.S. Pat. No. 3,876,885 discloses a series of relays for controlling the functioning of controlled units. The relays are interconnected so as to provide that when one is operated, others will not. Alterable time delay arrangements are provided whereby the sequence of the subsequent operation of the various relays can be controlled. The sequence is in part regulated by differences in the release time of time delaying-relay systems designed so that preferences among relays will change. Catterall does not disclose a relay system employing limited power output and switching means that may be hand-held in the manner contemplated by the instant invention.